The present invention relates generally to control of switching devices and, more particularly, to a driver and method to implement desired switching controls.
Driving a load between alternating high and low voltages can be employed to control electrical current in that load. This is often referred to Pulse Width Modulation (PWM). Usually, a PWM scheme utilizes two power switches coupled across a load. The switches are selectively activated from high to low conditions or from low to high conditions, taking precautions against having both switches fully ON at the same time.
Various power applications can employ a PWM scheme to provide desired current and/or voltage control to an associated load. One particular application relates to a spindle motor, such as is employed to rotate information platters, such as hard disk drives, CD-ROM drives, video tape recorders, etc. A three-phase dc motor is a common type of spindle motor, which, for example, has current energizing respective coils using a full wave bridge configuration. The bridge includes six power stages, with respective pairs of such stages being associated with each phase of the motor. Thus, one stage of each pair of stages and associated power devices are connected between the motor coil and ground, usually referred to as xe2x80x9clow sidexe2x80x9d stages. The other stage of each pair of stages and their power devices are referred to as xe2x80x9chigh sidexe2x80x9d stages and devices because they are connected between the power supply and the motor coil.
The power devices are operated as switches in a sequence that allows pulses of current to flow from the power supply through a high-side power device, a coil of the first of the three stages, a coil of the second of the three stages, and then through a low-side power device to ground. This process is repeated in a generally well-known manner for the other power devices and coil pairs to achieve three-phase energization from a single, direct current, power supply.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
One aspect of the present invention relates generally to a predriver for switching applications. The predriver includes an input for receiving control information and an output that provides an output signal for implementing control of an associated switch device. The control information can trigger a change in the output signal, such as from a first generally stable level to a second generally stable level. During the change in the output signal between levels, the predriver operates in at least two transitional modes to control the output signal. For example, the predriver can cause the output signal to change at different rates in each of the transitional modes. By controlling the rate of change in the output signal in the transition modes, the predriver can mitigate flyback and/or provide slew rate control for the associated switch device.
Several predrivers, in accordance with an aspect of the present invention, further can be used in a system to facilitate operation of a motor (e.g., a spindle motor) having one or more phases. For example, associated pairs of predrivers can be connected to control respective pairs of switch devices of a switching system, in which each pair of switch devices is connected across an associated phase of the motor. The predrivers can control the transition between generally stable (e.g., HIGH and LOW) operating levels of their respective output signals, in accordance with an aspect of the present invention, to provide corresponding output signals to respective switch devices so as to achieve desired characteristics in the motor system.
Another aspect of the present invention relates to a method of controlling a switch device. The method includes providing an output signal at one of first and second generally stable operating levels, such as for operating an associated switch device in one of first and second states. The output signal is controlled according to at least two different rates during a change between states of the output signal, such as can be inititated by an associated control system.
The following description and the annexed drawings set forth certain illustrative aspects of the invention. These aspects are indicative, however, of but a few ways in which the principles of the invention may be employed. Other advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.